Issue 16, 2016

Vibronic coupling in the excited-states of carotenoids

Abstract

The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2 to the optically dark state S1. Extending this picture, some additional dark states (3Ag and 1Bu) and their interaction with the S2 state have also been suggested to play a major role in the ultrafast deactivation of carotenoids and their properties. Here, we investigate the interaction between such dark and bright electronic excited states of open chain carotenoids, particularly its dependence on the number of conjugated double bonds (N). We focus on the ultrafast wave packet motion on the excited potential surface, which is modified by the interaction between bright and dark electronic states. Such a coupling between electronic states leads to a shift of the vibrational frequency during the excited-state evolution. In this regard, pump-degenerate four-wave mixing (pump-DFWM) is applied to a series of carotenoids with different numbers of conjugated double bonds N = 9, 10, 11 and 13 (neurosporene, spheroidene, lycopene and spirilloxanthin, respectively). Moreover, we demonstrate in a closed-chain carotenoid (lutein) that the coupling strength and therefore the vibrational shift can be tailored by changing the energy degeneracy between the 1B+u and 1Bu states via solvent interaction.

Graphical abstract: Vibronic coupling in the excited-states of carotenoids

Supplementary files

Article information

Article type
Paper
Submitted
07 Dec 2015
Accepted
23 Mar 2016
First published
23 Mar 2016

Phys. Chem. Chem. Phys., 2016,18, 11443-11453

Author version available

Vibronic coupling in the excited-states of carotenoids

T. Miki, T. Buckup, M. S. Krause, J. Southall, R. J. Cogdell and M. Motzkus, Phys. Chem. Chem. Phys., 2016, 18, 11443 DOI: 10.1039/C5CP07542D

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